1. Field of the Invention
The present invention relates to an apparatus for controlling an internal combustion engine for use in an automobile, which is capable of preventing shock or surging occurring when the automobile runs in the low speed region.
2. Description of the Related Art
In an internal combustion engine for use in an automobile, which has a fuel injection control system, and in which the injection time, i.e., the amount of the fuel to be injected, is determined according to the load of the engine (intake of air or pressure in a suction pipe) and the number of revolutions of the engine, it is known that deceleration shock or surging (fluctuation of acceleration) occurs when a throttle valve is abruptly closed for the purpose of decelerating the automobile running at the low speed. This phenomenon results from the fact that the intake of air (or the pressure in the suction pipe) is sharply reduced due to the abrupt closing of the throttle valve and accordingly the injection time, which is originally calculated based on the intake of air, is also extremely reduced. As a result, the air/fuel ratio of mixture within a combustion chamber becomes large and over-lean condition is brought about, so that the necessary torque is not generated and a so called minus torque is caused. This minus torque resonates with a characteristic frequency of the automobile to produce a shock or surging. To prevent this, in the Japanese Patent Laid-open Publication No. 59-231144, for example, when a throttle valve is closed under a certain operational condition, the injection time is maintained at the value just existing before the closure of the throttle valve for a predetermined duration, and after that the injection time is slowly shortened.
Further, there is an internal combustion engine, in which, upon engine braking, fuel is cut if the number of revolutions of the engine is higher than a predetermined value. When the injection of fuel is restarted, the control of decreasing fuel is undertaken in order to prevent acceleration shock caused by the abrupt increase of fuel. In such a control, fuel which has adhered to an inner wall of a suction pipe is completely evaporated during the fuel cut and, after restart of injection, injected fuel is consumed to wet the inner wall of the suction pipe, so that the over-lean condition is temporarily caused in a combustion chamber. This also results in occurrence of shock or surging. To prevent the shock or surging of this kind, in the Japanese Patent Laid-open Publication No. 60-30446, for example, the injection time is increased by a predetermined rate, after it was once decreased upon restart of the injection.
In the prior art as described above, whether the shock or surging is actually occurring or not, the control for preventing the shock or surging, i.e., the enrichment of fuel, is always executed in the deceleration process of the automobile. Therefore, the prior art is in danger of deteriorating the performance of purification of exhaust gas. Besides, the prior art provides no effect against the surging which occurs during a constant speed running of the automobile, which is caused by the irregular combustion in the engine, the condition of a road surface and so on.